This invention relates to a biological filter apparatus and to a method of operating a biological filter apparatus.
U.S. Pat. No. 5,518,920 discloses a filter unit for treating biodegradable volatile organic compounds (VOCs). The filter unit includes a filter bed of organic compost containing a population of microorganisms that have an affinity for VOCs and consume VOCs and nutrients present in the compost. Air laden with the volatile organic compounds passes upwards through the filter bed and the microorganisms biologically convert the VOCs to non-toxic form, typically carbon dioxide and water. The filter bed is kept in a warm and moist condition by periodically spraying water onto the filter bed from above and by warming the air that flows into the filter bed. In this manner, favorable conditions for establishing and maintaining the population of microorganisms in the filter bed are provided.
Although the filter described in U.S. Pat. No. 5,518,920 is effective, there is nevertheless room for improvement in performance of the filter.
In accordance with a first aspect of the invention there is provided a filter apparatus for processing air laden with volatile organic compounds, said apparatus comprising a first wall means defining a first filter chamber and a second filter chamber, a first air inlet for admitting air to the first filter chamber, a first air outlet for exhausting air from the first filter chamber, a second air inlet, connected to said first air outlet, for admitting air leaving the first filter chamber to the second filter chamber, and a second air outlet for exhausting air from the second filter chamber, a biologically inert filter media in the first filter chamber, a biologically active filter media in the second filter chamber, a water supply means for supplying water to an upper region of the first filter chamber, a second wall means defining a sump for receiving water from a lower region of the second filter chamber, and a recirculation means for feeding water from the sump to the water supply means, whereby water received from the lower region of the second filter chamber is supplied to the upper region of the first filter chamber for wetting the biologically inert filter media.
In accordance with a second aspect of the invention there is provided a method of operating a filter for processing air laden with biodegradable volatile organic compounds, said method comprising (a) passing the air sequentially through first and second filter beds, the first filter bed containing a biologically inert filter media and the second filter bed containing a biologically active filter media, water being present in said biologically active filter media and said biologically inert filter media, (b) collecting water that drains from the second filter bed, and (c) supplying water collected in step (b) to the first filter bed.